Sure you can. A cheetah is gold and an elephant is grey. See how easy that was. You can compare anything to anything. People today for some reason only understand scientific comparisons in which a single variable is isolated. I blame the education system for pushing "math and science" the last decade or so. A scientific comparison is only one specific type of comparison. A poet will compare a brunette womans hair to the "midnight winter sky". Even though the night sky and black hair are two different things!